Given the thread from Cooperplace fitting a BB7 on Road bike (frame is custom XACD Ti frame) uses a fork that was built for the bike, and with my interest in achieving the same end for my "Winter Bike", I have some queries re the end effect of fitting either a 26" MTB fork or CX Fork that is capable of accepting a disc.

The key differences seem to be the following ;1. The MTB or CX forks have a longer Axle to Crown distance of around 410mm (I think the typical 700C road bike is between 365 and 374mm)2. Rake is either 43 or 47mm (Typical road bike including mine is 45mm)

Sheldon's take is interesting - Fork Lengths by D Rinard, but this seems to deal more with minor changes, rather than ones that may bee seen with a CX/MTB style fork.

I guess the big question is, is there a ROAD DISC capable fork that isn't custom made ?

Plenty of road forks are 43 degree and the kinesis crosslight disc fork, which is cheap from crc is a 45 degree option anyway.

I guess you'll have to either search extensively, or select one of 43/400 (dc19) or 45/410 (crosslight), as the best replacement for your fork. Looks like your head angle would change by about 1.5 - 2 degrees, which would still likely see it at least 1 degree steeper than my MTB, which after all has to turn on single track, which is much tighter than anything I do on the road. I imagine you would be able to feel the difference though.

I get the impression that it's not so much the rake of the fork, but the overall trail that makes the difference (i.e. distance between the centre of the axle and the centre line of a straight line taken down through the steerer when projected to the ground).

...so sit down with a pencil and paper and have a guess / get as close as you can get.

In practice - as long as the front wheel doesn't strike your frame (or your feet) just ride it!

So we get the leaders we deserve and we elect, we get the companies and the products that we ask for, right? And we have to ask for different things. – Paul Gildingbut really, that's rubbish. We get none of it because the choices are illusory.

I've read the change is approx a degree per inch difference, so a 395mm fork would be a bit over 1 degree. Reading this, I now understand why my answer here won't really apply to you. For now, like drubie said, just get something from what is available then worry about getting a closer match later when a better selection of road forks are available. The UCI have already changed their mind allowing disc brakes for CX. Who knows, maybe they'll allow disc brakes on road bikes in the future.

You could have a play around on BikeCAD (which is a free applet) by inputting your frame's geometry and that of the forks you are looking at. That will just give you some numbers which might give you an idea, with some research, about how handling might be affected.

In reality though I expect the the difference between the forks will be minimal. All those forks are designed to go on standard road bikes and whether you have a 43 or 45 degree rake and few mm change in length won't matter much in the real world. You might feel the change, but nothing will go mad.

Hi guys, will have a play with the options available and measure the trail and rake that I have, and then see what the end resulting head tube angle, rake and trail is to see what the end difference is.

Thanks for the input Nobody, will have a closer look at the options you suggested

HT angle 73Âº, not unusual43mm rake is pretty standard for a modern road bike fork, 45mm not unusual at all, especially for a slightly lager frame.

The only really change you'd notice and be annoyed by is if the fork crown length was so long that it propped the front of the bike up to the extent that the HT angle was effectively flattened out, say to 71Âº. At which point you find find the trail lengthened appreciably and the steering wallowed around like an old pig.

Have contacted Wound Up, and they responded by asking what was the required Axle crown height, and that the rake wasn't an issue, so may be a positive outcome ?

Will give Bike CAD a go and see what the effect is.

Hi Michael,

just checked the Wound Up prices, not cheap. XACD was cheaper for a custom Ti fork. ANd it seems gorgeous to ride on. I keep on thinking, where is some bumpy road so I can find out how well it rides, but of course, I'm on the same old bits of bumpy road. it seems to give a smoother ride than CF. But it doesn't seem to flex at all. V happy with it.

drubie wrote:I get the impression that it's not so much the rake of the fork, but the overall trail that makes the difference (i.e. distance between the centre of the axle and the centre line of a straight line taken down through the steerer when projected to the ground).

yep. increasing trail (which will tend to happen as you increase rake) means more effort is required to overcome angular momentum (gyroscopic precession) of the front wheel. it's like a lever, the distance of which (rake) is the line between the steering axis (steering tube) and a parallel line that passes through the front axle. the longer the lever, the harder you have to push. but that also goes for other steering inputs, such as bumps in the road, so the more stable the bike is as well. in order to provide greater stability, MTBs have longer rake than roadies.

I'm still tossing up what fork to get (weight vs budget vs geometry changes), but have plunked for a hub ($35) from eBay, but looking at a DT Swiss/XT wheelset in 700C to use as a starting point, and then build up soomething at the end.

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